Effects of carbon source and carbon content on electrochemical performances of Li4Ti5O12/C prepared by one-step solid-state reaction

Li₄Ti₅O₁₂/C composites were synthesized by one-step solid-state reaction method using four commonly used organic compounds or organic polymers as carbon source, i.e., polyacrylate acid (PAA), citric acid (CA), maleic acid (MA) and polyvinyl alcohol (PVA). The physical characteristics of Li₄Ti₅O₁₂/C composites were investigated by X-ray diffraction, electron microscopy, Raman spectroscopy, particle size distribution and thermogravimetry-derivative thermogravimetry techniques. Their electrochemical properties were characterized by cyclic voltammograms, electrochemical impedance spectra, constant current charge–discharge and rate charge–discharge. These analyses indicated that the carbon source and carbon content have a great effect on the physical and electrochemical performances of Li₄Ti₅O₁₂/C composites. An ideal carbon source and appropriate carbon content effectively improved the electrical contact between the Li₄Ti₅O₁₂ particles, which enhanced the discharge capacity and rate capability of Li₄Ti₅O₁₂/C composites. PAA was the best carbon source for the synthesis of Li₄Ti₅O₁₂/C composites. When the carbon content was 3.49 wt.% (LiOH·H₂O/PAA molar ratio of 1), as-prepared Li₄Ti₅O₁₂/C showed the maximum discharge capacity. At 0.2 C, initial capacity of the optimized sample was 168.6 mAh g⁻¹ with capacity loss of 2.8% after 50 cycles. At 8 and 10 C, it showed discharge capacities of 143.5 and 132.7 mAh g⁻¹, with capacity loss of 8.7 and 9.9% after 50 cycles, respectively.     

Quartz crystal microbalance study of the growth of indium(III) sulphide films from a chemical solution

The growth of indium(III) sulphide thin films from aqueous thioacetamide (TA)-In(III) solution has been studied with a quartz crystal microbalance (QCM). It is found that the growth of the film consists in the parallel deposition of In₂S₃ and In₂O₃. Both processes are induced by sulphide anions (S²⁻) produced after decomposition of thioacetamide. In₂S₃ is deposited by precipitation of crystallites formed in the bulk solution. On stirred solutions this reaction is hindered due to the disruption of the nucleation centres. On the other hand, In₂O₃ is deposited by electrochemical reduction of naturally dissolved oxygen (O₂) by the S²⁻ anions, followed by chemical reaction with In³⁺. This process is of electroless-chemical nature and has important consequences on the properties of the films. Both reaction mechanisms, chemical and electroless-chemical, compete under different experimental conditions: temperature, solution composition, stirring. For instances, the deposit of In₂O₃ is favoured at low bath temperature, in aerated solutions, giving rise to films with higher oxide proportion. Additives like hydrochloric acid and acetic acid also favour In₂O₃ deposition. The system has easy possibility to tune chemical and physical properties of the films, like composition, transparency and absorption edge, of interest for photovoltaic applications.     

Effect of ZnO modification on the performance of LiNi0.5Co0.25Mn0.25O2 cathode material

ZnO was coated on LiNi_0.5Co_0.25Mn_0.25O₂ cathode (positive electrode) material for lithium ion battery via sol–gel method to improve the performance of LiNi_0.5Co_0.25Mn_0.25O₂. The X-ray diffraction (XRD) results indicated that the lattice structure of LiNi_0.5Co_0.25Mn_0.25O₂ was not changed distinctly after surface coating and part of Zn²⁺ might dope into the lattice of the material. Energy dispersive spectroscopy (EDS) and X-ray photoelectron spectroscopy (XPS) proved that ZnO existed on the surface of LiNi_0.5Co_0.25Mn_0.25O₂. Charge and discharge tests showed that the cycle performance and rate capability were improved by ZnO coating, however, the initial capacity decreased dramatically with increasing the amount of ZnO. Differential scanning calorimetry (DSC) results showed that thermal stability of the materials was improved. The XPS spectra after charge–discharge cycles showed that ZnO coated on LiNi_0.5Co_0.25Mn_0.25O₂ promoted the decomposition of the electrolyte at the early stage of charge–discharge cycle to form more stable SEI layer, and it also can scavenge the free acidic HF species from the electrolyte. The electrochemical impedance spectroscopy (EIS) results showed ZnO coating could suppress the augment of charge transfer resistance upon cycling.     

Electrochemical properties of LiNiO2 cathode after TiO2 or ZnO addition

LiNiO₂ was prepared by solid state reaction, and LiNiO₂ was mixed with 1-, 2-, or 5 wt% TiO₂ or ZnO for the preparation of cathodes for a lithium ion battery. The electrochemical properties of the cathodes were investigated and the effects of the addition of TiO₂ or ZnO were discussed. The voltage vs. capacity curves for charge and discharge at different numbers of cycles for LiNiO₂, 2 wt% TiO₂-added LiNiO₂, and 2 wt% ZnO₂-added LiNiO₂ showed that in all the samples the first discharge capacity is much smaller than the first charge capacity. The addition of TiO₂ or ZnO decreased the discharge capacities, but improved the cycling performance. The discharge capacities of LiNiO₂ and 2 wt% TiO₂-added LiNiO₂ decreased as the number of cycles increased. However, the discharge capacity of 2 wt% ZnO-added LiNiO₂ increased overall as the number of cycles increased. The −dx/|dV| vs. voltage curves for the 1st and 2nd cycles of 0, 1-, 2-, or 5 wt% TiO₂ or ZnO-added LiNiO₂ showed that all the samples underwent four phase transitions during charging and discharging.     

Preparation and characterization of core–shell structure Fe3O4/C nanoparticles with unique stability and high electrochemical performance for lithium-ion battery anode material

Core–shell structure carbon coating Fe₃O₄ nanoparticles are prepared by a two-step method. The crystalline structure and the electrochemical performance of the prepared samples are investigated. The results indicate that a uniform and continuous carbon layer is formed on the surface of Fe₃O₄ nanoparticles. The core–shell structure Fe₃O₄/C nanoparticles show a high initial discharge capacity of 1546 mAh g⁻¹ and a specific stable discharge capacity of about 800 mAh g⁻¹ at 0.5 C with no noticeable capacity fading up to 100 cycles.     

Eutectic crystallization in the UO2–Al2O3–HfO2 ceramic phase diagram

In the frame of the Generation IV Sodium Fast Reactor (SFR) safety studies, a core catcher with a sacrificial material could be placed at the bottom of the nuclear reactor. Its role is to dilute the (U, Pu)O₂ molten fuel in case of a hypothetical core meltdown accident. A Al₂O₃–HfO₂ ceramic is a candidate for the sacrificial material. To understand how the molten fuel would mix with this sacrificial material, the UO₂–Al₂O₃–HfO₂ system was investigated at CEA Cadarache PLINIUS corium platform. The eutectic position of the UO₂–Al₂O₃–HfO₂ was determined: the eutectic temperature is 1728±22 °C (2001±22 K) and the eutectic composition is 30 wt% UO₂–35 wt% Al₂O₃–35 wt% HfO₂. Then, the pseudo-binary UO₂–(50 wt% Al₂O₃–50 wt% HfO₂) phase diagram has been proposed.     

Low-temperature growth of well-crystalline Co3O4 hexagonal nanodisks as anode material for lithium-ion batteries

Uniform hexagonal-shaped cobalt oxide (Co₃O₄) nanodisks were prepared in large scale via facile aqueous solution based hydrothermal process at 110 °C. The detailed structural characterizations confirmed that the synthesized products are hexagonal cobalt oxide nanodisks, possessing very well-crystalline cubic spinel structure. A coin cell of type −2032 was assembled using the synthesized Co₃O₄ nanodisks and its charge–discharge profile was analyzed between the voltages 0.01 and to 2.5 V vs. Li/Li⁺ reference electrode. The electrochemical cell composed of Li/Co₃O₄ delivered an initial lithium insertion capacity of 2039 mAh/g. Although the cell exhibited high irreversible capacity during the first four cycles, the columbic efficiency has been improved upon cycling.     

Studying the influence of nano-Al2O3 particles on the corrosion performance and hydrolytic degradation resistance of an epoxy/polyamide coating on AA-1050

The aim of this work was studying the effects of addition of Al₂O₃ nanoparticles on the anticorrosion performance of an epoxy/polyamide coating applied on the AA-1050 metal substrate. For this purpose, the epoxy nanocomposites were prepared using 1, 2.5 and 3.5 (w/w) pre-dispersed surface modified Al₂O₃ nanoparticles. Field-emission electron microscope (FE-SEM) and ultraviolet–visible (UV–Vis) techniques were utilized in order to evaluate the nanoparticles dispersion in the epoxy coating matrix. The anticorrosion performance of the nanocomposites was studied by electrochemical impedance spectroscopy (EIS) (in 3.5 wt% NaCl solution for 135 days immersion) and salt spray test for 1000 h. The coating resistance against hydrolytic degradation was also studied by optical microscope and Fourier-transform infrared spectroscopy (FTIR). Results obtained from FE-SEM micrographs and UV–visible spectra showed that the nanoparticles dispersed in the coating matrix uniformly with particle size less than 100 nm even at high loadings. Results revealed that nano-Al₂O₃ particles could significantly improve the corrosion resistance of the epoxy coating. Nanoparticles reduced water permeability of the coating and improved its resistance against hydrolytic degradation.     

Electrochemical properties of bare and Ta-substituted Nb2O5 nanostructures

In this work, bare and Ta-substituted Nb₂O₅ nanofibers are prepared by electrospinning followed by sintering at temperatures in the 800–1100 °C range for 1 h in air. Obtained bare and Ta-substituted Nb₂O₅ polymorphs are characterized by X-ray diffraction, scanning electron microscopy, density measurement, and Brunauer, Emmett and Teller surface area. Electrochemical properties are evaluated by cyclic voltammetry and galvanostatic techniques. Cycling performance of Nb₂O₅ structures prepared at temperature 800 °C, 900 °C, and 1100 °C shows following discharge capacity at the end of 10th cycle: 123, 140, and 164 (±3) mAh g⁻¹, respectively, in the voltage range 1.2–3.0 V and at current rate of 150 mA g⁻¹ (1.5 C rate). Heat treated composite electrode based on M-Nb₂O₅ (1100 °C) in argon atmosphere at 220 °C, shows an improved discharge capacity of 192 (±3) mAh g⁻¹ at the end of 10th cycle. The discharge capacity of Ta-substituted Nb₂O₅ prepared at 900 °C and 1100 °C showed a reversible capacity of 150, 202 (±3) mAh g⁻¹, respectively, in the voltage range 1.2–3.0 V and at current rate of 150 mA g⁻¹. Anodic electrochemical properties of M-Nb₂O₅ deliver a reversible capacity of 382 (±5) mAh g⁻¹ at the end of 25th cycle and Ta-substituted Nb₂O₅ prepared at 900 °C, 1000 °C and 1100 °C shows a reversible capacity of 205, 130 and 200 (±3) mAh g⁻¹ (at 25th cycle) in the range, 0.005–2.6 V, at current rate of 100 mA g⁻¹.     

Electrochemical performances of Bi based compound film-coated ZnO as anodic materials of Ni–Zn secondary batteries

Microstructures and electrochemical performances of Bi based compound film-coated ZnO are investigated and compared with those of Ni film-coated ZnO and Bi nanocompound-modified ZnO in order to illuminate the coating effect of Bi based compound film. Bi based compound film is composed of nanoparticles (1–2 nm in diameter) of Bi₆(NO₃)₄(OH)₂O₆, BiO and Bi₂O₃, containing lots of micropores. In comparison with Bi nanocompound-modified ZnO and Ni film-coated ZnO, Bi based compound film-coated ZnO shows higher discharge capacity and more stable cycling performance. The highest average discharge capacity is as high as 535 mAh g⁻¹, and the discharge capacity does not obviously decrease during the cycling tests. Cyclic voltammograms indicates that Bi based compound film can limit transfer of H₂O, OH⁻, and enhance electrochemical activity of ZnO. The improvement of cycling performance is due to: (1) the coating film structure avoids the direct contact between ZnO/Zn with the electrolyte, and suppresses the dissolution of ZnO/Zn; (2) the micropores in the film is beneficial to adequate diffusion of H₂O, OH⁻ and zincates ions, leading to high discharge capacity and good cycling performance; (3) the light weight of the film also has a contribution to high specific discharge capacity.     

Synthesis of LiNi0.9Co0.1O2 from Li2CO3, NiO or NiCO3, and CoCO3 or Co3O4 and their electrochemical properties

Cathode active materials with a composition of LiNi_0.9Co_0.1O₂ were synthesized by a solid-state reaction method at 850 °C using Li₂CO₃, NiO or NiCO₃, and CoCO₃ or Co₃O₄, as the sources of Li, Ni, and Co, respectively. Electrochemical properties, structure, and microstructure of the synthesized LiNi_0.9Co_0.1O₂ samples were analyzed. The curves of voltage vs. x in Li_xNi_0.9Co_0.1O₂ for the first charge–discharge and the intercalated and deintercalated Li quantity Δx were studied. The destruction of unstable 3b sites and phase transitions were discussed from the first and second charge–discharge curves of voltage vs. x in Li_xNi_0.9Co_0.1O₂. The LiNi_0.9Co_0.1O₂ sample synthesized from Li₂CO₃, NiO, and Co₃O₄ had the largest first discharge capacity (151 mA h/g), with a discharge capacity deterioration rate of −0.8 mA h/g/cycle (that is, a discharge capacity increasing 0.8 mA h/g per cycle).     

Microwave-hydrothermal synthesis of Fe-based materials for lithium-ion batteries and supercapacitors

Fe-based materials, Fe₂O₃, Fe₃O₄, and FeOOH, were synthesized by the microwave–hydrothermal process in the temperature range of 100–200 °C and under very short reaction times of 15 min to 2 h. Under microwave-controlled hydrolysis and redox reactions, cube-like Fe₂O₃ was crystallized using FeCl₃, Fe₃O₄ particles were crystallized from FeCl₂ and FeOOH nanorods were crystallized using FeCl₃. The Fe-based materials were fabricated to make anodes and cathodes of lithium-ion battery and supercapacitor electrode materials to study their potential electrochemical applications. The electrochemical results showed that FeOOH had better anode capacity as lithium-ion batteries than those of Fe₂O₃ and Fe₃O₄. The present results suggest that the microwave–hydrothermally synthesized Fe-based materials are promising lithium-ion battery anode materials.     

Electrochemical properties of LiCoyMn2−yO4 synthesized using a combustion method in a voltage range of 3.5–5.0 V

LiCo_yMn_2−yO₄ (y = 0.00, 0.04 and 0.08) were synthesized using a combustion method, and the electrochemical properties were examined in the voltage range of 3.5–5.0 V. The XRD patterns of the synthesized samples were similar, and the samples had a spinel phase structure. The first charge capacity curves exhibited an inflection in the voltage range of 4.2–5.0 V, where it is believed that additional, previously unreported phase transition occurs. The voltage vs. x curves for the first to fifth cycle exhibited two distinct voltage plateaus, corresponding well to a two-phase reaction and a one-phase reaction, respectively, as reported previously. For the voltage range of 3.5–5.0 V, the first discharge capacity increased and the cycling performance improved as y increased. Among these samples, LiCo_0.08Mn_1.92O₄ had the largest first discharge capacity of 132.5 mA h/g at 600 μA/cm², and its cycling efficiency was 91.1% at the 15th cycle in the voltage range of 3.5–5.0 V.     

Nanocomposite Fe2O3-Se as a new lithium storage material

The electrochemical properties of nanocomposite Fe₂O₃-Se thin film prepared by pulsed laser deposition (PLD) method have been investigated by cyclic voltammetry and charge/discharge measurements. A large reversible capacity of nanocomposite Fe₂O₃-Se thin film was found to be around 650 mAh g⁻¹. A new couple of reduction and oxidation peaks at 1.4 and 1.8 V were observed from cyclic voltammogram for the first time. Our data demonstrated that nanocomposite Fe₂O₃-Se exhibit larger capacity and better cycle performance than pure Fe₂O₃. The electrochemical reaction mechanisms of Fe₂O₃-Se with lithium were examined by X-ray photoelectron spectroscopy (XPS), high resolution transmission electron microscopy (HRTEM) and selected-area electron diffraction (SAED). The reversible conversions reaction of nanosized metal Fe with Li₂Se and Li₂O formed after initial discharge process into FeSe and Fe₂O₃ respectively were revealed.     

Deterioration Mode of Barium-Containing NOx Storage Catalyst

Barium-containing NO _x storage catalyst showed serious deactivation under thermal exposure at high temperatures. To elucidate the thermal deterioration of the NO _x storage catalyst, four types of model catalyst, Pt/Al₂O₃, Ba/Al₂O₃, Pt–Ba/Al₂O₃, and a physical mixture of Pt/Al₂O₃ + Ba/Al₂O₃ were prepared and their physicochemical properties such as BET, NO TPD, TGA/DSC, XRD, and XPS were evaluated while the thermal aging temperature was increased from 550 to 1050°C. The fresh Pt–Ba/Al₂O₃ showed a sorption capacity of 3.35 wt%/g-cat. but the aged one revealed a reduced capacity of 2.28 wt%/g-cat. corresponding to 68% of the fresh one. It was found that this reduced sorption capacity was directly related to the deterioration of the NO _x storage catalyst by thermal aging. The Ba on Ba/Al₂O₃ and Pt–Ba/Al₂O₃ catalysts began to interact with alumina to form Ba–Al solid alloy above 600°C and then transformed into stable BaAl₂O₄ having a spinel structure. However, no phase transition was observed in the Pt/Al₂O₃ catalyst having no barium component, even after aging at 1050°C.     

Optical band gap modulation by Mg-doping in In2O3(ZnO)3 ceramics

In this study, different amounts of Mg were doped in In₂O₃(Zn_1−xMg_xO)₃ and their thin films were grown by using the RF magnetron sputtering method. The optical and electrical characteristics of the films revealed that the lattice constant decreased while the optical band gap increased as the Mg content increased, showing an inverse proportional relationship with each other. Therefore, it was found that Mg doping in indium zinc oxide (IZO) is also effective for band gap modulation as it was reported in a Mg-doped ZnO system. When IZO thin films were grown in a more reducing ambient, the carrier concentration increased which resulted in the increase of band gap energy. This was explained due to the Burstein–Moss effect.     

α-Fe2O3@CNSs nanocomposites as superior anode materials for lithium-ion batteries

The nanocomposite of hematite@carbon nanosprings (α-Fe₂O₃@CNSs) was synthesized by simple precipitation and following heat treatment, in which the amount of α-Fe₂O₃ can be easily controlled by changing the synthesis conditions. Thermogravimetric analysis (TGA), X-ray diffraction (XRD), scanning electronic microscopy (SEM), Brunau–Emmertt–Teller (BET), and X-ray photoelectron spectroscopy (XPS) were employed to characterize the as-synthesized nanocomposite. When applied as anode in Li-ion batteries (LIBs), the effect of α-Fe₂O₃/CNSs weight ratio on electrochemical performance of α-Fe₂O₃@CNSs nanocomposite has been researched. Enhancing the amount of α-Fe₂O₃ in nanocomposite would make the increase of specific capacity, but led to the degradation of cyclic stability and rate capability. The electrode of S-FeC (with weight ratio of CNSs/α-Fe₂O₃ about 4:1) could deliver a charge capacity of 527.6 mAh g⁻¹at 0.2 C with excellent cyclability (96.9% capacity retention after 50 cycles), and retained 343.3 mAh g⁻¹even at the rate of 5.0 C. In comparison with pure CNSs and α-Fe₂O₃, the improved cycling performance, specific capacity and rate capability of S-FeC should be mainly attributed to the combined effects of uniformly dispersed nanosized α-Fe₂O₃ particles and the highly strong network of CNSs.     

Variation of LiNiO<Subscript>2</Subscript> cathode properties with substitution of Ga,In and Tl by the combustion method

LiNi_1-y M_yO₂ (M = Ga, In and Tl, y = 0.010, 0.025 and 0.050) with small y were synthesized by the combustion method by calcining in an O₂ stream at 750 °C for 36 h. XRD analyses, SEM observation and measurement of the variation of discharge capacity with the number of cycles were carried out. All the samples had the Rm structure and LiNi_1-y In _y O₂ contained LiInO₂ phase as an impurity. Among LiNi_1-y Ga _y O₂ the sample with y = 0.025 had a relatively large first discharge capacity (172.2 mAh g⁻¹) and relatively good cycling performance (discharge capacity 140.3 mAh g⁻¹ at n = 20). For LiNi_0.975M_0.025O₂ (M = Ga, In and Tl), the first discharge capacity decreased in the order of the substituted element Ga, In and Tl. The variations of cation mixing and hexagonal ordering with the substituted element (decrease in I₀₀₃/I₁₀₄ and increase in R-factor from M = Ga through M = Tl) are considered to lead to the behavior of the first discharge capacity with the substituted element. LiNi_0.975Tl_0.025O₂ had the smallest degradation rate of the discharge capacity.     

Low temperature sintering and microwave dielectric properties of CaSiO3–Al2O3 ceramics for LTCC applications

The effects of CuO, Li₂CO₃ and CaTiO₃ additives on the densification, microstructure and microwave dielectric properties of CaSiO₃–1 wt% Al₂O₃ ceramics for low-temperature co-fired applications were investigated. With a single addition of 1 wt% Li₂CO₃, the CaSiO₃–1 wt% Al₂O₃ ceramic required a temperature of at least 975 °C to be dense enough. Large amount addition of Li₂CO₃ into the CaSiO₃–1 wt% Al₂O₃ ceramics led to the visible presence of Li₂Ca₃Si₆O₁₆ and Li₂Ca₄Si₄O₁₃ second phases. Fixing the Li₂CO₃ content at 1 wt%, a small amount of CuO addition significantly promoted the sintering process and lowered the densification temperature to 900 °C whereas its addition deteriorated the microwave dielectric properties of CaSiO₃–1 wt% Al₂O₃ ceramics. Based on 10 wt% CaTiO₃ compensation in temperature coefficient, good microwave dielectric properties of ε_r=8.92, Q×f=19,763 GHz and τ_f=−1.22 ppm/°C could be obtained for the 0.2 wt% CuO and 1.5 wt% Li₂CO₃ doped CaSiO₃–1 wt% Al₂O₃ ceramics sintered at 900 °C. The chemical compatibility of the above ceramics with silver during the cofiring process has also been investigated, and the result showed that there was no chemical reaction between silver and ceramics, indicating that the as-prepared composite ceramics were suitable for low-temperature co-fired ceramics applications.